Sleep deprivation is associated with significant social, financial, and health costs due to impaired cognitive performance. Chronic sleep restriction experiments demonstrate that cognitive deficits accumulate over time without full awareness by the affected individual. Functional neuroimaging reveals that frequent and progressively longer cognitive lapses involve changes in brain regions including the frontal and parietal cortices, secondary sensory processing areas, and the thalamus. Individual differences in cognitive vulnerability to sleep loss may be influenced by genetic variations regulating sleep homeostasis and circadian rhythms. Sleep deprivation increases the risk of human-error-related accidents, with an estimated annual economic impact of $43 to $56 billion. Motor vehicle accidents related to fatigue and drowsy driving are particularly common and often underestimated. Sleep deprivation impairs psychomotor performance, with effects equivalent to those induced by alcohol consumption. Sleep deprivation also affects attention, working memory, and higher cognitive abilities, with cognitive performance becoming progressively worse over time. Functional neuroimaging techniques such as PET and fMRI have been used to study the neural mechanisms underlying sleep deprivation. These studies show that sleep deprivation reduces metabolic rates in the frontal and temporal lobes, thalamus, basal ganglia, and cerebellum. fMRI studies reveal decreased activation in the prefrontal cortex, parietal lobe, and premotor cortex during attention and memory tasks. Sleep deprivation also impairs visual short-term memory and limits its capacity, affecting hippocampal activity during episodic memory encoding. Individual differences in cognitive vulnerability to sleep loss are systematic and trait-like, suggesting an underlying genetic component. Chronic partial sleep restriction, common in modern society, results in cumulative adverse effects on neurobehavioral functions, including increased daytime sleep propensity, decreased cognitive speed/accuracy, and increased attention lapses. Sleep restriction studies suggest that cumulative deficits in cognitive functions are more likely to occur when sleep is reduced below 7 hours per night, but individual differences in basal sleep need and resistance to sleep loss must be considered.Sleep deprivation is associated with significant social, financial, and health costs due to impaired cognitive performance. Chronic sleep restriction experiments demonstrate that cognitive deficits accumulate over time without full awareness by the affected individual. Functional neuroimaging reveals that frequent and progressively longer cognitive lapses involve changes in brain regions including the frontal and parietal cortices, secondary sensory processing areas, and the thalamus. Individual differences in cognitive vulnerability to sleep loss may be influenced by genetic variations regulating sleep homeostasis and circadian rhythms. Sleep deprivation increases the risk of human-error-related accidents, with an estimated annual economic impact of $43 to $56 billion. Motor vehicle accidents related to fatigue and drowsy driving are particularly common and often underestimated. Sleep deprivation impairs psychomotor performance, with effects equivalent to those induced by alcohol consumption. Sleep deprivation also affects attention, working memory, and higher cognitive abilities, with cognitive performance becoming progressively worse over time. Functional neuroimaging techniques such as PET and fMRI have been used to study the neural mechanisms underlying sleep deprivation. These studies show that sleep deprivation reduces metabolic rates in the frontal and temporal lobes, thalamus, basal ganglia, and cerebellum. fMRI studies reveal decreased activation in the prefrontal cortex, parietal lobe, and premotor cortex during attention and memory tasks. Sleep deprivation also impairs visual short-term memory and limits its capacity, affecting hippocampal activity during episodic memory encoding. Individual differences in cognitive vulnerability to sleep loss are systematic and trait-like, suggesting an underlying genetic component. Chronic partial sleep restriction, common in modern society, results in cumulative adverse effects on neurobehavioral functions, including increased daytime sleep propensity, decreased cognitive speed/accuracy, and increased attention lapses. Sleep restriction studies suggest that cumulative deficits in cognitive functions are more likely to occur when sleep is reduced below 7 hours per night, but individual differences in basal sleep need and resistance to sleep loss must be considered.